1. Field of the Invention
The present invention relates to a geomagnetism sensing device that detects geomagnetism by sensors respectively directed in three orthogonal directions and in particular, to a geomagnetism sensing device that can accurately calculate an angular velocity or the like when a magnetism sensing section with sensors mounted therein has turned in a three-dimensional space.
2. Description of the Related Art
A geomagnetism sensing device that detects geomagnetism by using a three-axis magnetic sensor which detects magnetic field strength in three directions which are at right angles to each other has been used as a rotation detection device, a posture sensing device, or the like.
A magnetic gyro described in Japanese Unexamined Patent Application Publication No. 2008-224642 has a three-axis magnetic sensor for detecting geomagnetism, which is disposed on a three-axis orthogonal coordinate. When the magnetic gyro is rotated in a three-dimensional space, a difference vector between two different points of time is sought using output data of three axes and whether or not the difference vector becomes smaller than a predetermined threshold is determined, whereby around what axis among the three axes the rotation has been made is specified.
When the magnetic gyro described in Japanese Unexamined Patent Application Publication No. 2008-224642 is rotated around any axis of three axes, which have been determined by the direction of the magnetic sensor, it is possible to detect a rotational state. However, when the magnetic gyro is rotated around an axis other than the three axes, a rotational axis cannot be recognized, such that in what rotational plane the rotation has been made cannot be specified. That is, only by a single magnetic gyro described in Japanese Unexamined Patent Application Publication No. 2008-224642, it is difficult to detect an angular velocity when rotation has been made around an arbitrary axis in a three-dimensional space.
A magnetic gyro described in PCT Japanese Translation Patent Re-Publication WO2007/099599 is provided with a memory that accumulates data of magnetic vectors which are detected in a time-series manner by a three-axis magnetic sensor, and a rotational axis is calculated on the basis of the data of the magnetic vectors at three or more different points of time accumulated in the memory and also a rotational velocity centered around the calculated rotational axis is calculated.
However, in the magnetic gyro described in PCT Japanese Translation Patent Re-Publication WO2007/099599, since the data of the magnetic vectors at three or more points of time are obtained in a state where there is no standard in a space, if an offset component is superimposed on the data or a noise is superimposed on the data, it is not possible to correct variations in individual data, such that it becomes difficult to specify an accurate rotational axis.